HA5024 Intersil Corporation, HA5024 Datasheet - Page 7

• Manufacturer Part Number: HA5024
• Description: Quad 125MHz Video Current Feedback Amplifier with Disable
• Manufacturer: Intersil Corporation

Application Information
Optimum Feedback Resistor
The plots of inverting and non-inverting frequency response,
see Figure 11 and Figure 12 in the Typical Performance
Curves section, illustrate the performance of the HA5024 in
various closed loop gain configurations. Although the
bandwidth dependency on closed loop gain isn’t as severe
as that of a voltage feedback amplifier, there can be an
appreciable decrease in bandwidth at higher gains. This
decrease may be minimized by taking advantage of the
current feedback amplifier’s unique relationship between
bandwidth and R
feedback resistor, even for unity gain applications, and R
conjunction with the internal compensation capacitor, sets
the dominant pole of the frequency response. Thus, the
amplifier’s bandwidth is inversely proportional to R
HA5024 design is optimized for a 1000 R
Decreasing R
resulting in excessive peaking and overshoot. At higher
gains the amplifier is more stable, so R
in a trade-off of stability for bandwidth.
The table below lists recommended R
gains, and the expected bandwidth.
PC Board Layout
The frequency response of this amplifier depends greatly on
the amount of care taken in designing the PC board. The
use of low inductance components such as chip resistors
and chip capacitors is strongly recommended. If leaded
components are used the leads must be kept short
especially for the power supply decoupling components and
those components connected to the inverting input.
Attention must be given to decoupling the power supplies. A
large value (10 F) tantalum or electrolytic capacitor in
parallel with a small value (0.1 F) chip capacitor works well
in most cases.
A ground plane is strongly recommended to control noise.
Care must also be taken to minimize the capacitance to
ground seen by the amplifier’s inverting input (-IN). The
larger this capacitance, the worse the gain peaking, resulting
in pulse overshoot and possible instability. It is
recommended that the ground plane be removed under
traces connected to -IN, and that connections to -IN be kept
as short as possible to minimize the capacitance from this
node to ground.
GAIN (A
+10
-10
+1
+2
+5
-1
CL
)
F
in a unity gain application decreases stability,
F
. All current feedback amplifiers require a
R
1000
1000
750
681
383
750
F
( )
7
F
F
BANDWIDTH (MHz)
values for various
can be decreased
F
at a gain of +1.
100
125
95
52
65
22
F
. The
F
, in
HA5024
Driving Capacitive Loads
Capacitive loads will degrade the amplifier’s phase margin
resulting in frequency response peaking and possible
oscillations. In most cases the oscillation can be avoided by
placing an isolation resistor (R) in series with the output as
shown in Figure 6.
The selection criteria for the isolation resister is highly
dependent on the load, but 27 has been determined to be
a good starting value.
Power Dissipation Considerations
Due to the high supply current inherent in quad amplifiers,
care must be taken to insure that the maximum junction
temperature (T
exceeded. Figure 7 shows the maximum ambient temperature
versus supply voltage for the available package styles (Plastic
DIP, SOIC). At 5V
styles may be operated over the full industrial range of -40
to 85
take into account output power, be performed by the designer.
Enable/Disable Function
When enabled the amplifier functions as a normal current
feedback amplifier with all of the data in the electrical
specifications table being valid and applicable. When
disabled the amplifier output assumes a true high
impedance state and the supply current is reduced
significantly.
FIGURE 6. PLACEMENT OF THE OUTPUT ISOLATION
FIGURE 7. MAXIMUM OPERATING AMBIENT TEMPERA-
130
120
110
100
o
90
80
70
60
50
C. It is recommended that thermal calculations, which
V
IN
5
RESISTOR, R
TURE vs SUPPLY VOLTAGE
J,
see Absolute Maximum Ratings) is not
DC
R
7
100
T
R
I
quiescent operation both package
SUPPLY VOLTAGE ( V)
+
-
9
PDIP
R
F
R
SOIC
11
C
13
L
V
OUT
15
o
C